The present invention is related to an improved method for forming stacked electronic components and an improved electronic component formed thereby. More specifically, the present invention is related to a method of forming stacked electronic components wherein the contact between the lead and external termination are less susceptible to thermal fluctuations as realized during assembly and use of the electronic component.
Methods for stacking and attaching lead frames to multilayered ceramic capacitors (MLCC) is well documented in the prior art. Even with the advanced understanding significant challenges remain. Thermal shock resistance and temperature cycling robustness remain a challenge due to coefficient of thermal expansion (CTE) mismatches between the lead frame and the solder materials used to attach the lead frame to the external terminations of the MLCC. This problem is exasperated by temperature requirements which are increasing from the current requirements, of up to 200° C., to future requirement of 250° C. and even up to 350° C. Capacitance-stable high temperature base metal electrode (BME) MLCC's have been developed and proven reliable at 200° C. Studies by Shaddock et. al. in “Reliability Assessment of Passives for 300° C. and 350° C.”from IMAPS High Temperature Electronics Network (HiTEN 2011) Jul. 18-20, 2011, Oxford, UK, have shown promising results with a calcium zirconate based dielectric compatible with nickel electrodes at 300° C. and 350° C. The challenge remains to find a lead attachment material that can withstand these extreme temperatures and which allow temperature cycling from −55° C. to high temperatures, exceeding 200° C., without cracking the MLCC at the solder/MLCC end-metallization interface.
Methods for attaching multiple MLCC's in a vertical stack have been documented in the prior art. These methods typically involve using solder attachments or conductive adhesive attachments. Most conductive adhesives degrade above 180° C. and are therefore not suitable for high temperature applications. Welding or wire bonding may also be used to form an electrical connection, but the mechanical strength, especially shear strength, is low. Many of these materials cannot withstand extreme temperature, have undesirable properties at high temperatures or cannot withstand extended cycling to extreme temperatures.
The stacking methods documented in the art typically involve a multitude of tooling configurations in order to accommodate the various numbers of chips in a stack to meet the capacitance need for a specific application. This is an expensive and inflexible process.
There is an ongoing desire to provide a method of forming stacked electronic components, particularly stacked MLCC's which can withstand the temperatures realized during solder reflow.